The axes on a Hertzsprung-Russell (H-R) diagram represent ________
A) mass and radius B) luminosity and surface temperature
C) mass and luminosity D) luminosity and apparent brightness
B
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The half-life of cobalt-60 is 5.3 years, while that of strontium-90 is about 29 years
Suppose you have samples of both isotopes, and that they initially contain equal numbers of atoms of these isotopes. How will the activities (number of decays per second) of the samples compare? A) The activities will be equal. B) The activity of the cobalt-60 sample will be greater. C) The activity of the strontium-90 sample will be greater. D) The activities cannot be compared without more information.
If a metallic wire of cross-sectional area 3.0 × 10^-6 m2 carries a current of 9.1 A and has a mobile charge density of 4.24 × 10^28 carriers/m3, what is the average drift velocity of the mobile charge carriers? (charge value = 1.6 × 10^-19 C)
a. 3.4 × 10^3 m/s c. 4.5 × 10^-4 m/s b. 1.7 × 10^3 m/s d. 1.5 × 10^-4 m/s
Carbon dioxide gas at 1 atmosphere pressure it to be heated from 25°C to 75°C by pumping it through a tube bank at a velocity of 4 m/s. The tubes are heated by steam condensing within them at 200°C. The tubes have 10 mm OD, are in an in–line arrangement, have a longitudinal spacing of 15 mm and a transverse spacing of 17 mm. If 13 tube rows are required, what is the average heat transfer coefficient and what is the pressure drop of the carbon dioxide?
GIVEN
• In-line tube bank: condensing steam inside, CO2 outside
• CO2 temperatures
? In: (Tg,in) = 25°C
? Out: (Tg,out) = 75°C
• CO2 velocity (Us) = 4 m/s
• Steam temperature (Ts) = 200°C
• Tube outside diameter (D) = 10 mm = 0.01 m
• Longitudinal spacing (SL) = 15 mm = 0.015 m
• Transverse spacing (ST) = 17 mm = 0.017 m
• Number of tubes (N) = 13
FIND (a) The average heat transfer coefficient (hc) (b) The CO2 pressure drop (?p)
ASSUMPTIONS
• Steady state
• The thermal resistances of the condensing steam and the tube walls are negligible (tube wall temperature = Ts)
SKETCH
Which event marks the beginning of a supernova?
A) the sudden collapse of an iron core into a compact ball of neutrons B) the onset of helium fusion after a helium flash C) the beginning of neon fusion in an extremely massive star D) the sudden initiation of the CNO cycle